1. Field of the Invention
The present invention relates to a color image forming apparatus using electrophotography and particularly to an image forming apparatus capable of forming an electrostatic latent image.
2. Description of the Related Art
Among electrophotographic color image forming apparatuses, a so-called in-line system independently including image forming units for respective colors for fast printing has been known. The in-line system color image forming apparatus adopts a configuration that sequentially transfers images from the image forming units of respective colors to an intermediate transfer belt and collectively transfers the images onto a recording medium.
Such a color image forming apparatus causes misregistration (positional deviation) owing to mechanical factors in the image forming units of the respective colors when superimposing the images. In particular, in a configuration independently including laser scanners (optical scanning devices) and photosensitive drums for the respective colors, positional relationships between the laser scanners and the photosensitive drums differ among colors. Accordingly, laser scanning positions on the photosensitive drums cannot be synchronized, causing misregistration.
To correct the misregistration, in the above color image forming apparatus, misregistration correction control is executed. In Japanese Patent Application Laid-Open No. H07-234612, toner images for detection for respective colors are transferred from photosensitive drums onto an image carrier (intermediate transfer belt), and relative positions of the toner images for detection in scanning and conveying directions are detected using optical sensors and thereby misregistration correction control is executed.